In pattern forming processes using photolithography that are performed on semiconductor wafers, there are cases where peripheral parts of a pattern formation part are not exposed and resist remains at such peripheral parts. Since resist remaining at a peripheral part can peel off and become dust that adheres to the semiconductor wafer, it must be removed prior to entering a subsequent process. For removal of the unnecessary resist on peripheral parts of a semiconductor wafer, a method, wherein light, guided by a light guiding device, is illuminated onto a resist-removal portion and the illumination spot is moved across the resist-removal portion to expose the entire resist-removal portion, is used. With this exposure method, in order to expose the entirety of the resist-removal portion uniformly, it is required that the light emitting from the light guiding device be shaped to have a cross section of rectangular shape and that the illuminance be made uniform across the entire cross section of the emitting light.
As a prior art of such a light guiding device, there is, for example, the light guiding device disclosed in Japanese Patent Publication Laid-open (Tokukai) No. H10-74676. With the light guiding device of Japanese Patent Publication Laid-open (Tokukai) No. H10-74676, an aperture member, having a rectangular transmitting part and being installed on an illumination head, shapes the cross section of the light emitting from the light guiding device to a rectangular shape. Also, U.S. Pat. No. 4,964,692 discloses a light guiding device equipped with stem-like member with a core/clad structure (a clad cane element), which makes uniform the light emitting from a light emitting end face of an optical fiber bundle.